If all is well in the universe this should show something like this in your browser when visiting the CGI:

My Home Directory is /home/some/directory My Path is set to /bin;/usr/bin

DESCRIPTION

This module attempts to make using HTML templates simple and natural. It extends standard HTML with a few new HTML-esque tags - <TMPL_VAR>, <TMPL_LOOP>, <TMPL_INCLUDE>, <TMPL_IF> and <TMPL_ELSE>. The file written with HTML and these new tags is called a template. It is usually saved separate from your script - possibly even created by someone else! Using this module you fill in the values for the variables, loops and branches declared in the template. This allows you to separate design - the HTML - from the data, which you generate in the Perl script.

This module is licensed under the GPL. See the LICENSE section below for more details.

MOTIVATION

It is true that there are a number of packages out there to do HTML templates. On the one hand you have things like HTML::Embperl which allows you freely mix Perl with HTML. On the other hand lie home-grown variable substitution solutions. Hopefully the module can find a place between the two.

One advantage of this module over a full HTML::Embperl-esque solution is that it enforces an important divide - design and programming. By limiting the programmer to just using simple variables and loops in the HTML, the template remains accessible to designers and other non-perl people. The use of HTML-esque syntax goes further to make the format understandable to others. In the future this similarity could be used to extend existing HTML editors/analyzers to support HTML::Template.

An advantage of this module over home-grown tag-replacement schemes is the support for loops. In my work I am often called on to produce tables of data in html. Producing them using simplistic HTML templates results in CGIs containing lots of HTML since the HTML itself cannot represent loops. The introduction of loop statements in the HTML simplifies this situation considerably. The designer can layout a single row and the programmer can fill it in as many times as necessary - all they must agree on is the parameter names.

For all that, I think the best thing about this module is that it does just one thing and it does it quickly and carefully. It doesn't try to replace Perl and HTML, it just augments them to interact a little better. And it's pretty fast.

The Tags

Note: even though these tags look like HTML they are a little different in a couple of ways. First, they must appear entirely on one line. Second, they're allowed to "break the rules". Something like:

<IMG SRC="<TMPL_VAR NAME=IMAGE_SRC>">

is not really valid HTML, but it is a perfectly valid use and will work as planned.

The "NAME=" in the tag is optional, although for extensibility's sake I recommend using it. Example - "<TMPL_LOOP LOOP_NAME>" is acceptable.

If you're a fanatic about valid HTML and would like your templates to conform to valid HTML syntax, you may optionally type template tags in the form of HTML comments. This may be of use to HTML authors who would like to validate their templates' HTML syntax prior to HTML::Template processing, or who use DTD-savvy editing tools.

<!-- TMPL_VAR NAME=PARAM1 -->

In order to realize a dramatic savings in bandwidth, the standard (non-comment) tags will be used throughout the rest of this documentation.

<TMPL_VAR ?ESCAPE=1? NAME="PARAMETER_NAME">

The <TMPL_VAR> tag is very simple. For each <TMPL_VAR> tag in the template you call $template->param(PARAMETER_NAME => "VALUE"). When the template is output the <TMPL_VAR> is replaced with the VALUE text you specified. If you don't set a parameter it just gets skipped in the output.

Optionally you can use the "ESCAPE=1" option in the tag to indicate that you want the value to be HTML-escaped before being returned from output. This means that the ", <, >, and & characters get translated into &quot;, &lt;, &gt; and &amp; respectively. This is useful when you want to use a TMPL_VAR in a context where those characters would cause trouble. Example:

<INPUT NAME=param TYPE=TEXT VALUE="<TMPL_VAR NAME="param">">

If you called param() with a value like sam"my you'll get in trouble with HTML's idea of a double-quote. On the other hand, if you use ESCAPE=1, like this:

<INPUT NAME=param TYPE=TEXT VALUE="<TMPL_VAR ESCAPE=1 NAME="param">">

You'll get what you wanted no matter what value happens to be passed in for param. You can also write ESCAPE="1" and ESCAPE='1'. Substitute a 0 for the 1 and you turn off escaping, which is the default anyway.

<TMPL_LOOP NAME="LOOP_NAME"> </TMPL_LOOP>

The <TMPL_LOOP> tag is a bit more complicated. The <TMPL_LOOP> tag allows you to delimit a section of text and give it a name. Inside the <TMPL_LOOP> you place <TMPL_VAR>s. Now you pass to param() a list (an array ref) of parameter assignments (hash refs). The loop iterates over this list and produces output from the text block for each pass. Unset parameters are skipped. Here's an example:

Basically, each <TMPL_LOOP> gets an array reference. Inside the array are any number of hash references. These hashes contain the name=>value pairs for a single pass over the loop template.

Inside a <TMPL_LOOP>, the only variables that are usable are the ones from the <TMPL_LOOP>. The variables in the outer blocks are not visible within a template loop. For the computer-science geeks among you, a <TMPL_LOOP> introduces a new scope much like a perl subroutine call. Unlike perl, there are no global variables in the templates.

<TMPL_INCLUDE NAME="filename.tmpl">

This tag includes a template directly into the current template at the point where the tag is found. The included template contents are used exactly as if its contents were physically included in the master template.

The file specified can be a full path - beginning with a '/'. If it isn't a full path, the path to the enclosing file is tried first. After that the path in the environment variable HTML_TEMPLATE_ROOT is tried next, if it exists. Next, the "path" new() option is consulted. As a final attempt, the filename is passed to open() directly. See below for more information on HTML_TEMPLATE_ROOT and the "path" option to new().

As a protection against infinitly recursive includes, an arbitary limit of 10 levels deep is imposed. You can alter this limit with the "max_includes" option. See the entry for the "max_includes" option below for more details.

<TMPL_IF NAME="CONTROL_PARAMETER_NAME"> </TMPL_IF>

The <TMPL_IF> tag allows you to include or not include a block of the template based on the value of a given parameter name. If the parameter is given a value that is true for Perl - like '1' - then the block is included in the output. If it is not defined, or given a false value - like '0' - then it is skipped. The parameters are specified the same way as with TMPL_VAR.

Example Template:

<TMPL_IF NAME="BOOL">
Some text that only gets displayed if BOOL is true!
</TMPL_IF>

Now if you call $template->param(BOOL => 1) then the above block will be included by output.

<TMPL_IF> </TMPL_IF> blocks can include any valid HTML::Template construct - VARs and LOOPs and other IF/ELSE blocks. Note, however, that intersecting a <TMPL_IF> and a <TMPL_LOOP> is invalid.

If the name of a TMPL_LOOP is used in a TMPL_IF, the IF block will output if the loop has at least one row. Example:

<TMPL_IF LOOP_ONE>
This will output if the loop is not empty.
</TMPL_IF>
<TMPL_LOOP LOOP_ONE>
....
</TMPL_LOOP>

WARNING: Much of the benefit of HTML::Template is in decoupling your Perl and HTML. If you introduce numerous cases where you have TMPL_IFs and matching Perl if()s, you will create a maintenance problem in keeping the two synchronized. I suggest you adopt the practice of only using TMPL_IF if you can do so without requiring a matching if() in your Perl code.

<TMPL_ELSE>

You can include an alternate block in your TMPL_IF block by using TMPL_ELSE. NOTE: You still end the block with </TMPL_IF>, not </TMPL_ELSE>!

Example:
<TMPL_IF BOOL>
Some text that is included only if BOOL is true
<TMPL_ELSE>
Some text that is included only if BOOL is false
</TMPL_IF>

<TMPL_UNLESS NAME="CONTROL_PARAMETER_NAME"> </TMPL_UNLESS>

This tag is the opposite of <TMPL_IF>. The block is output if the CONTROL_PARAMETER is set false or not defined. You can use <TMPL_ELSE> with <TMPL_UNLESS> just as you can with <TMPL_IF>.

Example:
<TMPL_UNLESS BOOL>
Some text that is output only if BOOL is FALSE.
<TMPL_ELSE>
Some text that is output only if BOOL is TRUE.
</TMPL_UNLESS>

If the name of a TMPL_LOOP is used in a TMPL_UNLESS, the UNLESS block output if the loop has zero rows.

<TMPL_UNLESS LOOP_ONE>
This will output if the loop is empty.
</TMPL_UNLESS>
<TMPL_LOOP LOOP_ONE>
....
</TMPL_LOOP>

Methods

new()

You must call new() with at least one name => value pair specifying how to access the template text. You can use "filename => 'file.tmpl'" to specify a filename to be opened as the template. Alternately you can use:

These initialize the template from in-memory resources. In almost every case you'll want to use the filename parameter. If you're worried about all the disk access from reading a template file just use mod_perl and the cache option detailed below.

The three new() calling methods can also be accessed as below, if you prefer.

If the environment variable HTML_TEMPLATE_ROOT is set and your filename doesn't begin with /, then the path will be relative to the value of $HTML_TEMPLATE_ROOT. Example - if the environment variable HTML_TEMPLATE_ROOT is set to "/home/sam" and I call HTML::Template->new() with filename set to "sam.tmpl", the HTML::Template will try to open "/home/sam/sam.tmpl" to access the template file. You can also affect the search path for files with the "path" option to new() - see below for more information.

You can modify the Template object's behavior with new. These options are available:

die_on_bad_params - if set to 0 the module will let you call $template->param(param_name => 'value') even if 'param_name' doesn't exist in the template body. Defaults to 1.

strict - if set to 0 the module will allow things that look like they might be TMPL_* tags to get by without dieing. Example:

<TMPL_HUH NAME=ZUH>

Would normally cause an error, but if you call new with strict => 0, HTML::Template will ignore it. Defaults to 1.

cache - if set to 1 the module will cache in memory the parsed templates based on the filename parameter and modification date of the file. This only applies to templates opened with the filename parameter specified, not scalarref or arrayref templates. Caching also looks at the modification times of any files included using <TMPL_INCLUDE> tags, but again, only if the template is opened with filename parameter.

This is mainly of use in a persistent environment like Apache/mod_perl. It has absolutely no benefit in a normal CGI environment since the script is unloaded from memory after every request. For a cache that does work for normal CGIs see the 'shared_cache' option below.

Note that different new() parameter settings do not cause a cache refresh, only a change in the modification time of the template will trigger a cache refresh. For most usages this is fine. My simplistic testing shows that using cache yields a 90% performance increase under mod_perl. Cache defaults to 0.

shared_cache - *EXPERIMENTAL* - if set to 1 the module will store its cache in shared memory using the IPC::ShareLite and Storable modules (available from CPAN). The effect of this will be to maintain a single shared copy of each parsed template for all instances of HTML::Template to use. This can be a significant reduction in memory usage in a multiple server environment. As an example, on one of our systems we use 4MB of template cache and maintain 25 httpd processes - shared_cache results in saving almost 100MB! Of course, some reduction in speed versus normal caching is to be expected. Another difference between normal caching and shared_cache is that shared_cache will work in a CGI environment - normal caching is only useful in a persistent environment like Apache/mod_perl.

By default HTML::Template uses the IPC key 'TMPL' as a shared root segment (0x4c504d54 in hex), but this can be changed by setting the 'ipc_key' new() parameter to another 4-character or integer key.

On most unix systems you can examine the shared memory segments using 'ipcs' and delete them with 'ipcrm'. This can be necessary if for some reason the HTML::Template cache becomes corrupt. I've included a small script in scripts/ called clean_shm.pl. On my system this script deletes all shared memory segments accessible by the running user - sort of a "rm -rf /" for shared memory.

This option is currently *EXPERIMENTAL* - give it a try and tell me how it works out for you. I'm particularily interested in reports of how it works under heavy-load and on non-Linux systems.

blind_cache - if set to 1 the module behaves exactly as with normal caching but does not check to see if the file has changed on each request. This option should be used with caution, but could be of use on high-load servers. My tests show blind_cache performing only 1 to 2 percent faster than cache under mod_perl.

NOTE: Combining this option with shared_cache can result in stale templates stuck permanently in shared memory!

associate - this option allows you to inherit the parameter values from other objects. The only requirement for the other object is that it have a param() method that works like HTML::Template's param(). A good candidate would be a CGI.pm query object. Example:

The old associateCGI() call is still supported, but should be considered obsolete.

loop_context_vars - when this parameter is set to true (it is false by default) three loop context variables are made available inside a loop: __FIRST__, __LAST__ and __INNER__. They can be used with <TMPL_IF>, <TMPL_UNLESS> and <TMPL_ELSE> to control how a loop is output. Example:

<TMPL_LOOP NAME="FOO">
<TMPL_IF NAME="__FIRST__">
This only outputs on the first pass.
</TMPL_IF>
<TMPL_IF NAME="__INNER__">
This outputs on passes that are neither first nor last.
</TMPL_IF>
<TMPL_IF NAME="__LAST__">
This only outputs on the last pass.
<TMPL_IF>
</TMPL_LOOP>

One use of this feature is to provide a "separator" similar in effect to the perl function join(). Example:

Given an appropriate param() call, of course. NOTE: A loop with only a single pass will get both __FIRST__ and __LAST__ set to true, but not __INNER__.

path - you can set this variable with a list of paths to search for files specified with the "filename" option to new() and for files included with the <TMPL_INCLUDE> tag. This list is only consulted when the filename is relative - i.e. does not begin with a '/'. The HTML_TEMPLATE_ROOT environment variable is always tried first if it exists. In the case of a <TMPL_INCLUDE> file, the path to the including file is also tried before path is consulted.

max_includes - set this variable to determine the maximum depth that includes can reach. Set to 10 by default. Including files to a depth greater than this value causes an error message to be displayed. Set to 0 to disable this protection.

vanguard_compatibility_mode - if set to 1 the module will expect to see <TMPL_VAR>s that look like %NAME% in addition to the standard syntax. Also sets die_on_bad_params => 0. If you're not at Vanguard Media trying to use an old format template don't worry about this one. Defaults to 0.

debug - if set to 1 the module will write random debugging information to STDERR. Defaults to 0.

debug_stack - if set to 1 the module will use Data::Dumper to print out the contents of the parse_stack to STDERR. Defaults to 0.

cache_debug - if set to 1 the module will send information on cache loads, hits and misses to STDERR. Defaults to 0.

clear_params()

output()

output() returns the final result of the template. In most situations you'll want to print this, like:

print $template->output();

When output is called each occurrence of <TMPL_VAR NAME=name> is replaced with the value assigned to "name" via param(). If a named parameter is unset it is simply replaced with ''. <TMPL_LOOPS> are evaluated once per parameter set, accumlating output on each pass.

Calling output() is guaranteed not to change the state of the Template object, in case you were wondering. This property is mostly important for the internal implementation of loops.

FREQUENTLY ASKED QUESTIONS

In the interest of greater understanding I've started a FAQ section of the perldocs. Please look in here before you send me email.

1) Is there a place to go to discuss HTML::Template and/or get help?

There's a mailing-list for HTML::Template at htmltmpl@lists.vm.com. Send a blank message to htmltmpl-subscribe@lists.vm.com to join!

2) I want support for <TMPL_XXX>! How about it?

Maybe. I definitely encourage people to discuss their ideas for HTML::Template on the mailing list. Please be ready to explain to me how the new tag fits in with HTML::Template's mission to provide a fast, lightweight system for using HTML templates.

NOTE: Offering to program said addition and provide it in the form of a patch to the most recent version of HTML::Template will definitely have a softening effect on potential opponents!

3) I found a bug, can you fix it?

That depends. Did you send me the VERSION of HTML::Template, a test script and a test template? If so, then almost certainly.

If you're feeling really adventurous, HTML::Template has a publically available CVS server. See below for more information in the PUBLIC CVS SERVER section.

4) <TMPL_VAR>s from the main template aren't working inside a <TMPL_LOOP>! Why?

This is the intended behavior. <TMPL_LOOP> introduces a separate scope for <TMPL_VAR>s much like a subroutine call in Perl introduces a separate scope for "my" variables. If you need to have a variable from the main template work inside a loop you'll need to manually provide the value for each iteration of the loop.

5) Why do you use /[Tt]/ instead of /t/i? It's so ugly!

Simple - the case-insensitive match switch is very inefficient. According to _Mastering_Regular_Expressions_ from O'Reilly Press, /[Tt]/ is faster and more space efficient than /t/i - by as much as double against long strings. //i essentially does a lc() on the string and keeps a temporary copy in memory.

When this changes, and it is in the 5.6 development series, I will gladly use //i. Believe me, I realize [Tt] is hideously ugly.

Note that you'll need to modify the "return unless" line to specify the extension you use for your template files - I use .tmpl, as you can see. You'll also need to specify the path to your template files.

One potential problem: the "/path/to/templates/" must be EXACTLY the same path you use when you call HTML::Template->new(). Otherwise the cache won't know they're the same file and will load a new copy - instead getting a speed increase, you'll double your memory usage. To find out if this is happening set cache_debug => 1 in your application code and look for "CACHE MISS" messages in the logs.

7) What characters are allowed in TMPL_* NAMEs?

Numbers, letters, '.', '/', '+', '-' and '_'.

BUGS

I am aware of no bugs - if you find one, join the mailing list and tell us about it (htmltmpl@lists.vm.com). You can join the HTML::Template mailing-list by sending a blank email to htmltmpl-subscribe@lists.vm.com. Of course, you can still email me directly (sam@tregar.com) with bugs, but I reserve the right to forward said bug reports to the mailing list.

When submitting bug reports, be sure to include full details, including the VERSION of the module, a test script and a test template demonstrating the problem!

If you're feeling really adventurous, HTML::Template has a publically available CVS server. See below for more information in the PUBLIC CVS SERVER section.

CREDITS

This module was the brain child of my boss, Jesse Erlbaum (jesse@vm.com) here at Vanguard Media. The most original idea in this module - the <TMPL_LOOP> - was entirely his.

PUBLIC CVS SERVER

HTML::Template now has a publicly accessible CVS server provided by SourceForge (www.sourceforge.net). You can access it by going to http://sourceforge.net/cvs/?group_id=1075. Give it a try!

AUTHOR

Sam Tregar, sam@tregar.com (you can also find me on the mailing list at htmltmpl@lists.vm.com - join it by sending a blank message to htmltmpl-subscribe@lists.vm.com).

LICENSE

HTML::Template : A module for using HTML Templates with Perl

Copyright (C) 1999 Sam Tregar (sam@tregar.com)

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

1 POD Error

The following errors were encountered while parsing the POD:

Around line 623:

=back doesn't take any parameters, but you said =back 4

Module Install Instructions

To install HTML::Template, simply copy and paste either of the commands in to your terminal